Recently, attention is drawn to the technique of imprinting a pattern by pressing a mold with nanometer-sized (0.001 to 1 μm) irregularities (hereinafter, also referred to as a nanostructure) to a resin material applied on a substrate, namely, the nanoimprint technique. Studies have been made for application of that technique to optical materials, miniaturization of ICs, substrates for clinical examinations, and the like.
In nanometer-size microprocessing by a conventional photolithography technique, a shorter exposure wavelength is employed to solve insufficient resolution that is caused by diffraction occurring during exposure through a mask, which causes problems of complication of the device and cost increase. The nanoimprint technique allows easy formation of a nanometer-sized pattern by embossing, thereby solving these problems. Moreover, the nanoimprint technique may enable mass production of optical materials required to have a nanometer-sized microstructure, at low cost. With respect to a common embossing in which a pattern is not in a nanometer size, a product with a surface on which frosting is continuously formed and a frosting roll for producing the above product are known (see Patent Literature 1, for example).
Known methods used in the nanoimprint technique include a thermal nanoimprint technique and ultraviolet (UV) nanoimprint technique. In the UV nanoimprint technique, for example, an ultraviolet curable resin is applied to a substrate to form a thin film, and a mold having a nanostructure is pressed to the thin film. Then, the thin film is irradiated with ultraviolet rays to give a thin film (hereinafter, also referred to as a nanoimprint film) with a nanostructure in the inverse shape of that of the mold. When such methods are used at the research stage, a nanoimprint sheet is commonly produced by batch treatment using a plate-shaped mold.
For mass production of nanoimprint sheets by the nanoimprint technique at low cost, roll-to-roll treatment is more suitable than batch treatment. The reason for this is that, in the roll-to-roll treatment, a nanostructure can be formed on the outer peripheral surface of the mold roll so that nanoimprint sheets can be produced continuously for a longtime.
An exemplary optical material having a nanostructure is mentioned here. A known nanostructured body in optical materials is a “moth-eye structure”. The moth-eye structure includes a large number of protrusions spaced at an interval being sufficiently small relative to the visible light, between top points thereof. Examples of optical elements having a moth-eye structure include a transparent substrate with a surface on which a moth-eye structure is formed. With such a moth-eye structure, since the size ratio of the protrusion to the wavelength of the visible light is sufficiently small, protrusions formed allows visible light incident upon the surface of a transparent substrate to recognize that the refractive index successively changes from the air layer to the transparent substrate, and not to recognize the surface of the transparent substrate as an interface interrupting the refractive index. As a result, reflected light generated on the surface of the transparent substrate is significantly reduced.
In the field of technology for producing optical materials having such nanostructured bodies, a known method uses a mold that is an aluminum substrate with nanometer-sized holes formed on the surface by anodization. This method allows formation of nanostructured bodies that are distributed microscopically irregularly (at random) and are distributed macroscopically regularly. That is, employment of this method in production of an imprint roller allows formation of seamless nanostructured bodies, which is needed for continuous production, on the surface of a pillar- or cylinder-shaped mold roller. Anodization does not relate to the nanoimprint technique, and a known technique thereof include anodizing an aluminum layer optionally with masking on a portion thereof and then removing the anodized part of the aluminum layer (see Patent Literature 2, for example).